Carbon-based materials in the forms of strands, webs or fabrics have a variety of beneficial applications. Aerospace composites include carbon-based fabrics that are completely filled and typically contain 60 percent fiber by volume and are known to have remarkable structural capabilities. For example, carbon-epoxy or carbon-phenol fibers are used by those in the art. Stiffness is an asset for wings, helicopter rotor blades, golf clubs and tennis rackets. Further, pyrolytic carbon-based fabrics use carbon atoms to bind or bridge fibers together can be formed into brake rotors which are rigid in nature. Stiffness is also a key property to performance of such brake rotors at about 50 percent fiber by volume. However, for frictional materials, stiffness is undesirable as it localizes, intensifies and makes more cyclically acute the crush-loading, thermal-stress and twisted fiber and pair bundle stresses such as when utilized in continuous slip service applications.
In frictional materials of the prior art, these carbon fibers have been formed into a mat or woven together and immersed in or impregnated with an organic binder such as a phenolic resin. However, these prior art system as described hereafter have shortcomings in terms of their frictional properties, heat dissipation and structural integrity when fabricated into frictional devices.
Winckler, U.S. Pat. No. 4,700,823, discloses a locking differential including an oil lubricating clutch assembly having a plurality of interleaved friction discs formed of steel and squeezed together to retain rotation of differential side gears. Adjacent friction discs have mutually facing friction surfaces. One of each mutually facing friction surface is defined by the metal forming the disc and the another surface is defined by a pyrolytic carbon composite friction material. In one form, the friction material includes a mesh of cloth substrate formed of carbon fibers, which may be woven into a single layer of cloth, and a coating of carbon deposited on the fibers by chemical vapor deposition. The coating of carbon is sufficient to provide a friction material having a relatively open mesh which is readily penetrated by an adhesive to improve bonding of the friction material to the disc. Such adhesive is added for bonding to a disc and so that the adhesive penetrates the mesh but does not extrude completely through to the frictional surface of the material.
Bauer, U.S. Pat. No. 4,291,794, discloses a power transmission-energy absorption device and carbon composite friction facing material for use therein substantially the same as Winckler. This system includes a carbon composite friction membrane of fibrous material. The fibers of the material are carbonized or graphitized so that a pyrolytic material is deposited interstitially of the fibrous material. Thus, both Winckler and Bauer provide a mesh wherein oil flows along the surface of the mesh due to the texture provided by the woven pyrolytic carbon fibers.
Graham et al, U.S. Pat. No. 3,261,440 discloses clutch and brake assemblies with artificial graphite and organic resins and adhesives such as a furfural resin or phenol formaldehyde reins, or elemental carbon as a binder. The frictional material has a porosity which is preferably an interconnecting porosity and permeability. However, resins such as phenols are typically detrimental with oils because the phenol resin inherently generates a large lock-up spike. To overcome this additives are used in the oils, but these additives breakdown over time reverting to adversely effect performance of the friction material. Further, phenolic resins have excellent "wetting" characteristics which strongly encourages hydrodynamic low friction behavior.
Augustin, U.S. Pat. No. 3,927,241 discloses a dual layer clutch system having a first layer designed, by being compliant to distribute energy and a second layer designed for frictional properties. The frictional material includes carbon fibers impregnated with a phenol resin solution wherein the resin content is 60 percent.
The present invention provides advantages over the prior art.